Heres the question followed by the textbook answer from the back.
Im stuck on how it got the answer. Ive just done about 5 others in the same way, but this one doesn't seem to give me the right answer.
I did the correct method i think.
Heres the row of the pascal triangle i used:
1 6 15 20 15 6 1
So i basicly did:
... etc and simplified. I really don't understand how i got the answer wrong. Any suggestions?